A double clutch transmission having a countershaft design for implementing various transmission ratios for forward driving and travel in reverse, known from practical applications, is equipped with a central transmission shaft, a hollow transmission shaft disposed concentrically thereto, a countershaft, and two power-shift elements. Both of the power-shift elements are operatively connected on the input side to a drive assembly. One of the two power-shift elements is connected on the output side to the central transmission shaft, while the other of the two power-shift elements is connected on the output side to the hollow transmission shaft. The central transmission shaft and the hollow transmission shaft can be connected to the countershaft in order to implement a transmission ratio via gear stages that can be engaged into and disengaged from the power flow via shift devices. In addition, two gear stages are assigned to each of a plurality of shift devices.
A double clutch transmission comprising a double clutch, the input side of which can be driven by a drive shaft of a drive motor, and the output sides of which each have a drive connection to one of two coaxially disposed transmission input shafts, is known from DE 10 2005 005 163 A1. The double clutch transmission comprises an intermediate shaft, or exactly one countershaft, and has fixed gears and idler gears, which are fastened or rotatably supported on shafts, and shifting groups assigned to the idler gears. The idler gears can be connected to the particular dedicated shaft in a rotationally fixed manner via the shifting groups in order to implement transmission ratios or transmission ratio steps. The shifting groups are each assigned to two speeds, which are not in direct succession.
However, only seven transmission ratios for forward travel can be implemented using the two double clutch transmissions described above, thereby preventing drive motors, in particular internal combustion engines, that can be coupled to the double clutch transmissions, from being operated to the desired extent in the optimum operating range thereof in respect, in particular, to the available tractive force and low fuel consumption, across a large operating range of the drive motors.
Document DE 10 2007 049 271 A1 describes a double clutch transmission comprising at least two countershafts, in order to implement a plurality of transmission ratios for forward travel and travel in reverse.
Since the double clutch transmission is designed with two countershafts, a larger radial construction space is required therefore, as compared to double clutch transmissions comprising one countershaft; the larger radial construction space is not available to the necessary extent in various vehicle systems.